One of the most common types of implantable medical devices in use today is the implantable pacemaker. Modern pacemakers are small, battery-powered electronic devices that monitor the activity of the heart to determine when the heart is naturally beating, and provide stimulation pulses to the heart when the heart is not naturally beating, thereby maintaining a prescribed heart rhythm or rate. Advantageously, a pacemaker may be implanted in a patient, and coupled to the patient's heart via appropriate pacemaker leads that are also implanted. By implanting the pacemaker and leads, the pacemaker becomes an integral part of the patient, and the patient is able to maintain a substantially normal life style without the bother and worry that typically accompany the use of external (non-implanted), life-sustaining medical devices.
Nearly all implantable pacemakers in use today, as well as similar implantable medical devices, can be configured by the attending physician in the physician's office. The process of configuring a pacemaker is commonly referred to as "programming". The programming process uses non-invasive telemetry to customize the operation of the pacemaker to fit the individual needs of the patient. Customization is achieved by adjusting a set of "pacemaker parameters" to values that cause the pacemaker to work in an optimum way for the particular patient within whom the device has been implanted.
Disadvantageously, as the complexity of new implantable devices has evolved over the past several years, it has become increasingly difficult for the attending physician, or other medical personnel, to determine how the pacemaker should be programmed in order to provide the most effective therapy for a given patient. This difficulty is particularly manifest with recent-generation pacemakers that tend to be more automatic and autonomous than earlier-generation pacemakers, and that respond to input control signals from one or more sensors that attempt to assess the physiological needs of the patient.
A significant factor that makes the optimum programming of recent-generation pacemakers more difficult is the variation in each of the sensor inputs from patient to patient. Such variation is caused by numerous factors, including the patient's physical structure, age, sex, the implant site, the particular disease or malady the patient has and its progression within the patient's heart or other body tissue, the patient's physical condition and associated activity level, the drugs being taken by the patient to treat his or her condition, etc. Thus, to appropriately program the pacemaker for a given patient, the physician must anticipate how the pacemaker will operate given all of these variables, and given all the environments and activities that the patient is expected to encounter. Programming a modern pacemaker may thus comprise an extremely formidable task, for which task there is a critical need for programming aids to assist the physician in anticipating the pacemaker response for each particular patient.
An important aid known in the art to help properly program an implantable pacemaker, and to facilitate the physician's understanding of the pacemaker's programmed operation as its interacts with the patient's natural cardiac activity, is the sensing and recording of various pacemaker and cardiac events, including the rate of occurrence of such events (hereafter "event/rate data"). Once such event/rate data has been collected, it may be presented in a histogram format, as taught, e.g., in U.S. Pat. No. 4,513,743 (van Arragon et al.). The van Arragon '743 patent teaches various types of single-event histograms which display or show the distribution of a single event as a function of a specified class. The specified class may be, e.g., an atrial rate, with each class comprising a particular range of atrial rates, e.g., 0-50 ppm, 51-60 ppm, 61-70 ppm, etc. The van Arragon '743 patent further teaches that two such single event histograms may be shown in parallel, as shown in FIG. 3(d) of the '743 patent, or that a plurality of such single event histograms may be shown in series (time sequence), as shown in FIG. 3(e) of the '743 patent.
It is further known to display the event/rate data in an event count table, as taught, e.g., in U.S. Pat. No. 5,309,919 (Snell et al.), incorporated herein by reference. The Snell '919 patent teaches gathering of such event/rate data over a significant period of time, e.g., several hours, days, or months, and then (when requested by a physician or other medical personnel) downloading the event/rate data to the pacemaker's programming device ("programmer") for further processing and display. In particular, the Snell '919 patent teaches that such event/rate data, after having been gathered and downloaded, may be displayed in the form of an event/rate table. An event/rate table of the type created and displayed in the Snell '919 patent is shown, for example, in FIG. 6.
Unfortunately, the information conveyed in a conventional heart rate histogram, such as is taught in the van Arragon '743 patent, is somewhat incomplete because only a single event is displayed in each histogram, while other events are either not displayed, or must be displayed in a different histogram which is displayed separately, or in parallel, or in series with, other histograms. Such multiple single-event histogram displays, while potentially conveying a great deal of information, do not collectively convey such information in a format that is very easy for an attending physician (or other medical personnel) to readily comprehend, or that is easy to correlate with the other information. Further, while the data presented in an event/rate table, such as is developed in the Snell '919 patent, and is shown in FIG. 6 herein, is very complete, such data is not particularly easy to comprehend, visualize or correlate without careful analysis thereof.
In view of the above, it is evident that what is needed are improved techniques and methods of presenting existing event/rate data in a way that makes such event/rate data much easier to quickly comprehend and correlate, thereby facilitating its use in evaluating the performance of the patient's pacemaker. Once the data/rate information is properly understood, it thereafter serves a more useful purpose in correctly guiding subsequent reprogramming of the pacemaker, as required, and in aiding the development of appropriate treatment therapy for the patient.